Methods of defect inspection

ABSTRACT

Embodiments of the present disclosure relate to methods for defect inspection. After pattern features are formed in a structure layer, a dummy filling material having dissimilar optical properties from the structure layer is filled in the pattern features. The dissimilar optical properties between materials in the pattern features and the structure layer increase contrast in images captured by an inspection tool, thus increasing the defect capture rate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/833,640 filed Dec. 6, 2017, which claims priority to U.S. ProvisionalPatent Application Ser. No. 62/550,113, filed on Aug. 25, 2017, theentire content of each of which herein is incorporated by reference.

BACKGROUND

Semiconductor integrated circuits (ICs) are fabricated by a variety ofprocesses for patterning, deposition, removal, and modification. Qualityinspections are carried out during various stages of fabrication. Forexample, after-etch-inspection (AEI) is usually performed to monitorpattern defects in a patterning process.

However, as the dimension of the semiconductor integrated circuitshrinks, it becomes more challenging to capture defects usingtraditional defection inspection methods. Accordingly, there is a needfor an improved defect inspection method.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic flow chart of a method according to one embodimentof the present disclosure.

FIGS. 2A-2K are schematic partial views of a semiconductor device atvarious stages of fabrication according to embodiments of the presentdisclosure.

FIGS. 3A-3D are charts of optical properties of a structure layer and adummy filling material according to embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

FIG. 1 is a flow chart illustrating an exemplary method 100 forfabricating a semiconductor device according to various embodiments ofthe present disclosure. FIGS. 2A-2K are schematic partial views of asemiconductor structure 200 at various stages of fabrication accordingto the flow chart of FIG. 1. Those skilled in the art should recognizethat the full process for forming a semiconductor device and theassociated structures are not illustrated in the drawings or describedherein. Although various operations are illustrated in the drawings anddescribed herein, no limitation regarding the order of such steps or thepresence or absence of intervening steps is implied. Operations depictedor described as sequential are, unless explicitly specified, merely doneso for purposes of explanation without precluding the possibility thatthe respective steps are actually performed in concurrent or overlappingmanner, at least partially if not entirely.

The semiconductor structure 200 may be any suitable structures formed ona semiconductor substrate, such as a shallow trench isolation (STI)structure with diffusion regions (e.g., active regions) formedtherebetween, an interconnection structure with conductive andnon-conductive areas, a fin structure formed around shallow trenchisolation structure, such as a Fin Field Effect Transistor (FinFET)structure, a gate structure, a contact structure, a front-end structure,a back-end structure, or any other suitable structures utilized insemiconductor applications.

The method 100 begins with operation 105 by forming a pattern in aphotoresist layer 208 on a substrate 202, as shown in FIG. 2A. Exemplarymaterials for the substrate 202 include materials selected from at leastone of crystalline silicon, silicon oxide, strained silicon, silicongermanium, doped or undoped polysilicon, doped or undoped silicon wafersand patterned or non-patterned wafers silicon on insulator (SOI), carbondoped silicon oxides, silicon nitride, doped silicon, germanium, galliumarsenide, glass and sapphire. It is contemplated that the substrate 202is not limited to any particular size or shape. Therefore, the substrate202 may be a circular substrate having a 200 mm diameter, a 300 mmdiameter or other diameters, such as 450 mm, among others. The substrate202 may also be any polygonal, square, rectangular, curved or otherwisenon-circular workpiece.

The semiconductor structure 200 may include a first structure layer 204formed over the substrate 202. It is noted that additional structures,material layers, or device structures may be pre-formed on the substrate202 prior to forming the first structure layer 204 so as to facilitateoperation and proper function of the semiconductor device including thesemiconductor structure 200. For example, a front end structure, such asa gate structure, a contact structure, or other suitable structures maybe pre-formed on the substrate 202 prior to forming the first structurelayer 204.

The first structure layer 204 may be a doped oxide layer disposed arounda gate structure or an interlayer dielectric layer in an interconnectstructure. In some embodiments, the first structure layer 204 is a low-kdielectric layer, such as thermal silicon oxide, phosphorous-dopedsilicate glass(PSG), silicon oxyfluoride (FSG), hydrogen sislsesquioxane(HSQ), nanoporous silica, polyaryleneether (PAE), fluorinated amorphouscarbon (α-CF), or other materials suitable for use as an interlayerdielectric. In one embodiment, the first structure layer 204 is a PSGlayer formed by a chemical vapor deposition (CVD) process usingtetra-ethyl-ortho-silicate (TEOS) as a precursor.

A second structure layer 206 is formed over the first structure layer204. The second structure layer 206 may be any structure layer to bepatterned, for example to be patterned using a photoresist layer. Thesecond structure layer 206 may be an interlayer dielectric layer, a capoxide layer, a hard mask layer, a polysilicon layer, and the like. Thesecond structure layer 206 may be formed using any suitable techniques,such as a CVD process, a plasma enhanced chemical vapor depositionprocess (PECVD), or an epitaxial deposition process.

In some embodiments, the second structure layer 206 may be a siliconoxide layer, such as an un-doped silicate glass (USG) cap oxide layer.The USG cap oxide layer may be formed by a PECVD process using TEOS as aprecursor. In other embodiments, the second structure layer 206 may be asilicon nitride layer, a metal nitride layer, a silicone layer, or ametal oxide layer.

At operation 105, the photoresist layer 208 is coated over the secondstructure layer 206 to transfer a pattern to the second structure layer206. As shown in FIG. 2A, pattern features 210 are formed in thephotoresist layer 208 using a photolithography process, whereby ageometric pattern is transferred from a photomask to a photoresist layeron a substrate. The photolithography process may be performed over thewhole substrate 202 or over a portion of the substrate 202.

The photolithography process used in operation 105 may be any suitablephotolithography processes, such as ultraviolet (UV) photolithography,immersion photolithography, and ultraviolet (EUV) photolithographydepending on the minimum feature size, also called the criticaldimension (CD) of the pattern to be formed. The critical dimension ofthe pattern features 210 may be a diameter of the pattern feature whenthe pattern feature is a hole, a line width when the pattern feature 210is a line, or two times the half pitch of repeating pattern features210. In FIG. 2A, the pattern features 210 are holes having an afterdevelopment critical dimension 226. It should be noted that the patternfeatures 210 may be any suitable features to achieve intended functionsof the semiconductor structure 200.

In one embodiment, the critical dimension 226 of the pattern features210 may be less than about 30 nanometer. For example, the criticaldimension 226 of the pattern features 210 is in a range from about 30nanometer to about 16 nanometer. The pattern features 210 may be formedby an EUV photolithography. The EUV photolithography may be performedusing a light source having a wavelength about 13.5 nanometer or less.

During semiconductor manufacturing, an after-develop inspection (ADI)may be performed to monitor the patterning process and reduce patterningdefects in the photolithography process. However, after-developinspection is a challenging inspection because the pattern features inthe photoresist layer have low contrast and the transparent photoresistlayer can cause prior level defects to be confused with defects in thephotoresist layer. After-develop inspection becomes even morechallenging as the critical dimension shrinks, such as in the patternsformed by an EUV photolithography process. Embodiments of the presentdisclosure provide an inspection method for monitoring the patterningprocess after transferring the pattern features 210 in the photoresistlayer 208 to the second structure layer 206 beneath the photoresistlayer 208.

In operation 110, a suitable etch process is performed to transfer thepattern features 210 in the photoresist layer 208 to the secondstructure layer 206. Pattern features 212 are formed in the secondstructure layer 206 as shown in FIG. 2B. The pattern features 212 mayhave an after-etch critical dimension 228. Even though a differencebetween the critical dimension 228 and the critical dimension 226, knownas critical dimension (CD) bias, exists, operations are typically takento control CD bias and measurement of the critical dimension 228 can beused to monitor patterning defects in the patterning process.

The etch process may be a dry etch process. In one embodiment, anreactive ion etch (RIE) may be used to etch the second structure layer206 including silicon oxide formed by PECVD. Particularly, a mixture ofprocessing gases including carbon tetrafluoride (CF₄) and Carbontrifluoride (CHF₃) may be used in a RIE chamber to remove the secondstructure layer 206 using the patterned photoresist layer 208 as a mask.

The pattern features 212 also have a depth 230. In some embodiments, adepth 230 of the pattern features 212 is only a portion of an intendeddepth in production manufacturing. For example, during productionmanufacturing, an etch process performed after the photolithographyprocess in operation 105 would use the substrate 202 as an etch stop andend after etching through both the second structure layer 206 and thefirst structure layer 204. The etch process in operation 110 may stopwhen the depth 230 of the pattern features 212 is sufficient for aninspection tool to measure the after-etch critical dimension 228. Forexample, the depth 230 may be greater than about 1.5 of the criticaldimension 226. In some embodiments, the depth 230 may be between about1.5 to about 3.0 of the critical dimension 226. For pattern featureshaving a critical dimension of about 30 nanometer, the depth 230 may begreater than 45 nanometer, for example between about 45 nanometer toabout 90 nanometer.

The depth 230 may be achieved by controlling operation time usingestimated or measured etch rate. For example, the dry etch process usinga mixture of processing gases including carbon tetrafluoride (CF₄) andCarbon trifluoride (CHF₃) to silicon oxide formed by PECVD may beperformed for a period between 22 to 45 seconds when the estimated etchrate is about 2 nanometers/second.

As shown in FIG. 2B, the pattern features 212 may have a bottom surface232 in the first structure layer 204. Alternatively, the bottom surface232 of the pattern features 212 may be in the second structure layer206. Alternatively, the bottom surface 232 of the pattern features 212may be the substrate 202.

The semiconductor structure 200 as shown in FIG. 2B may be inspected atthis time for defects using an inspection tool during an after etchinspection (AEI). An inspection tool typically impinges a radiationtowards the semiconductor structure 200 and detects reflected and/orscattered radiation from the semiconductor structure 200 to generate anoptical image. The detected radiation depends on optical properties,such as refractive index of the surface structure. Because the patternfeatures 212 are hollow volumes in the second structure layer 206,optical properties of air reflect the patterned features 212 whileoptical properties of the second structure layer 206 reflect as thebackground. However, when the optical properties of the second structurelayer 206 are similar to that of air, it is difficult to distinguish thepattern features 212 from the background, i.e., the second structurelayer 206.

In operation 115, the pattern features 212 are filled with a dummyfilling material 214 as shown in FIG. 2C. The dummy filling material 214is selected so that the dummy filling material 214 and the secondstructure layer 206 have dissimilar optical properties to increasecontrast in the inspection results. In one embodiment, an opticalproperty of the dummy filling material 214 and the material in thesecond structure layer 206 is considered dissimilar when the differencein their optical properties is greater than a threshold value in aspectrum used by an inspection tool. For example, the threshold valuemay be in a range between about 10% to about 50% of the optical propertyvalue of the material in the second structure layer 206. In someembodiments, the threshold value may be about 30% of the opticalproperty value of the material in the second structure layer 206. Forexample, the dummy filling material 214 may be selected to have adissimilar complex refractive index, refractive index, extinctioncoefficient, permittivity, reflection coefficient, or combinationsthereof compared to the second structure layer 206. In some embodiments,the dummy filling material 214 is selected to have a dissimilarrefractive index to that of the second structure layer 206 in awavelength or spectrum used by an inspection tool. The dissimilarrefractive indexes enable increased contrast in an inspection imagethus, improving defect capture rate.

One of more optical properties, including but not limited to adissimilar complex refractive index, refractive index, extinctioncoefficient, permittivity, reflection coefficient, of the dummy fillingmaterial 214 are in a range from 0% to about 90% or in a range fromabout 110% to 1,000% of the same properties of the material in thesecond structure layer. For example, one of more optical properties,including but not limited to a dissimilar complex refractive index,refractive index, extinction coefficient, permittivity, reflectioncoefficient, of the dummy filling material 214 are in a range from 0% toabout 70% or in a range from about 130% to 250% of the same propertiesof the material in the second structure layer 206. In an embodiment, thepermissivity of the dummy filling material 214 is in a range from about130% and 250% of air.

In the case when the second structure layer 206 includes silicon oxide,the dummy filling material 214 may be a bottom anti-reflective coating(BARC) material, a silicon based material, such as amorphous silicon andsilicon nitride, a metal oxide, such as aluminum oxide and hafniumoxide, a metal nitride, such as titanium nitride and tantalum nitride, ametal, such as copper and tungsten, and combination thereof, or othersuitable materials with dissimilar optical properties. The dummy fillingmaterial 214 may be formed by a coating process, an atomic layerdeposition (ALD) process, a CVD process, a PVD process, or othersuitable processes for the material type.

Exemplary BARC material includes silicon oxide, silicon oxycarbide,silicon oxynitride, hydrocarbon-containing silicon oxide, siliconnitride, titanium nitride, tantalum nitride, titanium containingmaterial, tantalum containing material, an organic material, and anycombination thereof. The BARC material may be formed over the secondstructure layer 206 using any suitable technique, such as CVD, PECVD,high-density plasma CVD (HDP-CVD), or spin coating process.

In one embodiment, the dummy filling material 214 may be an organicpolymeric BARC, such as a highly cross-linking organic polymer known inthe industry as BARCs. In some embodiments, the dummy filling material214 includes BARCs with monomer units having hydroxyl groups. In someembodiments, the dummy filling material 214 includes BARCs with monomerunits that undergo hydration when exposed to water at a suitable pHvalue. In some embodiments, the dummy filling material 214 includesBARCs with monomer units that have alkenes, alkynes, or aromatic groups.In some embodiments, the dummy filling material 214 includes BARCscontaining ester, acrylate, or isocyanate monomers. In some embodiments,the dummy filling material 214 includes BARCs containing an acrylatepolymer or copolymer. In some embodiments, the dummy filling material214 includes BARCs containing an aromatic monomer. In some embodiments,the dummy filling material 214 includes BARCs containing a styrenepolymer or copolymer. In some embodiments, the dummy filling material214 includes BARCs containing hydroxyl groups, or capable of acquiringhydroxyl groups through a hydration reaction, can react with oxideabrasive particles in a dehydration reaction or bind to the abrasiveparticles through ether linkages during a CMP process.

In some embodiments, a BARC material, is selected as the dummy fillingmaterial 214 when the second structure layer 206 includes silicon oxideformed using TEOS precursor. The BARC material may be applied to thesecond structure layer 206 using a spin coating process.

In one embodiment, the second structure layer 206 includes silicon oxideformed using TEOS precursor and the dummy filling material 214 is anamorphous silicon. The amorphous silicon may be formed by a CVD process,for example with a CVD process using silane (SiH₄) gas as a siliconsource.

In operation 120, excess dummy filling material 214 on the secondstructure layer 206 in FIG. 2C is removed. After removal, the secondstructure layer 206 is exposed, as shown in FIG. 2D. In FIG. 2D, a topsurface 234 is exposed for inspection. The top surface 234 includes thesecond structure layer 206 and the dummy filling materials 214 inpattern features 216, which reflects the shape of the pattern features212 at the top surface 234.

FIG. 2E is a schematic top view of the semiconductor structure 200. FIG.2E shows the top surface 234 of the dummy filling material 214 in thepattern features 216 and the top surface of the second structure layer206 as the background areas. The pattern features 216 shown in FIG. 2Eare circular holes. It is noted that the pattern features 216 may belines, rectangular holes, or other suitable shapes reflecting thecorresponding pattern features 212.

In operation 120, the excess dummy filling material 214 may be removedusing a planarization process, such as a chemical mechanical polishing(CMP) process, or an etch process, such as an ashing process. An endpoint detection may be used in operation 120. For example, when a CMPprocess is used in operation 120, consumed polishing fluid may bemonitored for an end point. When the consumed polishing fluid includesboth materials from the second structure layer 206 and the dummy fillingmaterial 214 and a ratio of the dummy filling material 214 over thematerial from the second structure layer 206 reflects a ratio of patternareas and background areas, an end point of the CMP process is detected.Similarly, when an etch process is used in operation 120, an exhaustflow of the etch chamber may be monitored. When the exhaust flowincludes both by-products from etching the second structure layer 206and the by-products from etching the dummy filling material 214 and aratio of the by-products from the dummy filling material 214 over thebyproducts from the second structure layer 206 reflects a ratio ofpattern areas and background areas, an end point of the etching processis detected.

In one embodiment, the dummy filling material 214 includes an organicpolymeric BARC material, and the excess dummy filling material 214 maybe removed using an etch process, such as an etching process usingplasma of oxygen. In some embodiments, the dummy filling material 214includes amorphous silicon, and the excess dummy filling material 214may be removed using a CMP process.

In operation 125, the pattern features 216 may be inspected for defectsusing an inspection tool. The pattern features 216 may be inspected byimpinging a radiation towards the top surface 234 of the semiconductorstructure 200 shown in FIG. 2D and detecting radiation reflected and/orscattered by the semiconductor structure 200.

A suitable inspection tool may be a scanning surface inspection system(SSIS), such as a bright field imaging system and a dark field imagingsystem, a scanning electron microscope (SEM) system, an opticalmicroscope system, a scanning probe microscope system, a lasermicroscope system, a transmission microscope system, a focus ion beammicroscope system, or other suitable imaging system.

In operation 125, the semiconductor structure 200 is positioned in aninspection tool. The inspection tool impinges radiation in an inspectionwavelength or an inspection spectrum towards to the semiconductorstructure 200 in a scanning manner. The inspection tool detects theradiation reflected and/or scattered by the semiconductor structure 200to generate an optical image reflecting the top surface 234 as shown inFIG. 2E.

Because the dummy filling material 214 in the pattern features 216 andthe materials in the second structure layer 206 have dissimilarrefractive indexes, the image captured by the inspection tool alsoincludes a detectable contrast between the pattern features 216 and thesecond structure layer 206. The detectable contrast is especially usefulfor pattern features with a small critical dimension.

As discussed above, the dummy filling material 214 may be selected tohave a dissimilar optical property, such as complex refractive index,refractive index, extinction coefficient, permittivity, reflectioncoefficient, or combinations thereof, compared to the second structurelayer 206. When an electromagnetic wave propagates through a material,the material attenuates the electromagnetic wave. A complex refractiveindex n of a material is used to define how the material attenuateselectromagnetic waves passing through. Accordingly, the complexrefractive index of the second structure layer 206 may be used as abasis for selecting a dummy filling material. The larger the differencebetween the complex refractive indexes, the bigger the contrast betweenthe pattern areas and the background areas, i.e., second structure layer206, in the inspection image.

The complex refractive index n includes the real part n and theimaginary part κ:

n=n+iκ

The real part n is called the refractive index and indicates the phasevelocity. The imaginary part κ is called the extinction coefficient ormass attenuation coefficient and indicates the amount of attenuationwhen an electromagnetic wave propagates through a material. Thus, thereal part and/or the imaginary part of the complex refractive index nmay be used as a basis for selecting the dummy filling material 214.

Similarly, the relative permittivity ε_(r) or dielectric constant (K) ofa material can also be used to select the dummy filling material 214 asthe relative permittivity relates to the refractive index n and therelative magnetic permeability μ_(r):

n ²=ε_(r)μ_(r)

Since most material are only slightly magnetic μ_(r)≅1, and

ε_(r)≅√{square root over (n)}.

FIG. 3A is a chart of the refractive indexes n of a silicon oxide formedfor TEOS precursor, a BARC material, and air. Curve 302 is therefractive index of air for electromagnetic waves in the wavelengthbetween 2500 Å and 4000 Å. Curve 304 is the refractive index of asilicon oxide layer formed from TEOS precursor for electromagnetic wavesin the wavelength between 2500 Å and 4000 Å. Curve 306 is the refractiveindex of a BARC material for electromagnetic waves in the wavelengthbetween 2500 Å and 4000 Å. Spectrum 308 indicates an inspection spectrumof a suitable inspection tool. FIG. 3A illustrates the differencesbetween the refractive indexes of the BARC material and air are greaterthan the differences between the refractive indexes of silicon oxide andair, particularly within the spectrum 308. Because of the differences inrefractive indexes between the BARC material and silicon oxide, usingthe BARC material as the dummy filling material 214 increases inspectioncontrast compared to leaving the pattern features 212 hollow with air.

FIG. 3B is a chart of the attenuation coefficients K of a silicon oxideformed for TEOS precursor, a BARC material, and air. Curve 312 is theattenuation coefficient of air for electromagnetic waves in thewavelength between 2500 Å and 4000 Å. Curve 314 is the attenuationcoefficient of a silicon oxide layer formed from TEOS precursor forelectromagnetic waves in the wavelength between 2500 Å and 4000 Å. Curve316 is the attenuation coefficient of a BARC material forelectromagnetic waves in the wavelength between 2500 Å and 4000 Å.Spectrum 318 indicates an inspection spectrum of a suitable inspectiontool. As shown in FIG. 3B, the attenuation coefficients of air andsilicon oxide are substantially the same for electromagnetic wave in thewavelength between 2500 Å and 4000 Å. The differences between theattenuation coefficients of the BARC material and air are much greaterthan the differences between the attenuation coefficients of siliconoxide and air, particularly within the inspection spectrum. Because ofthe differences in attenuation coefficients between the BARC materialand silicon oxide, using the BARC material as the dummy filling material214 greatly increases inspection contrast compared to leaving thepattern features 212 hollow with air.

When selecting the dummy filling material, the refractive index and theattenuation coefficient can be considered separately or in combinationdepending on the material in the structure layer, operational mechanismof the inspection tool, critical dimension of the pattern features, andother relevant factors.

In some embodiments, the inspection spectrum or an inspection wavelengthmay be selected according to the differences between the refractiveindexes and/or the differences between the attenuation coefficients ofthe dummy filling material 214 in the pattern features 212 and thesecond structure layer 206 to capture the maximum contrast in theinspection images. For example, an inspection wavelength around 2700 Å,such as a wavelength between 2500 Å and 2800 Å may be used to inspectpattern features formed in a silicon oxide structure layer and filledwith a BARC material. Similarly, an inspection spectrum around 2700 Å,such as a spectrum of wavelengths between 2500 Å and 2800 Å may be usedto inspect pattern features formed in a silicon oxide structure layerand filled with a BARC material.

FIG. 3C is a chart of permittivity differences between two BARCmaterials and silicon oxide, and between air and silicon oxide. Curve322 is the permittivity difference between air and silicon oxide forelectromagnetic wave in the wavelength between 2500 Å and 3000 Å. Therelative permittivity of air is nearly constant across the spectrum.Curve 324 is the permittivity difference between a first BARC materialand silicon oxide for electromagnetic wave in the wavelength between2500 Å and 3000 Å. Curve 326 is the permittivity difference between asecond BARC material and silicon oxide for electromagnetic wave in thewavelength between 2500 Å and 3000 Å. The permittivity differencesbetween BARCs and silicon oxide fluctuate across the spectrum. The BARCmaterials may be used as a dummy filling material in pattern featuresformed in a material having similar permittivity as air, such as siliconoxide, to increase contrast in inspection images. When a suitableinspection wavelength is selected, such as a wavelength near 2600 Å, thefirst BARC material increases signal intensity by about 20%, and thesecond BARC material increases signal intensity or intensity of detectedelectromagnetic wave by about 75%.

FIG. 3D is a chart of the relative permittivity difference betweenamorphous silicon and silicon oxide comparing to the permittivitydifferences between the two BARC materials, air and silicon oxide. Curve328 is the permittivity difference between amorphous silicon and siliconoxide for electromagnetic wave in the wavelength between 2500 Å and 3000Å. As shown in FIG. 3D, the permittivity difference between amorphoussilicon and silicon oxide is about 20 times greater than thepermittivity difference between air and silicon oxide across thespectrum from 2500 Å and 3000 Å. When amorphous silicon is used as adummy filling material in pattern features formed in a material havingsimilar permittivity as air, the signal intensity or intensity ofdetected electromagnetic wave increases about twenty times.

The dissimilar optical properties between the second structure layer 206and the dummy filling material 214 in the pattern features 212 enableincreased contrast in the inspection image, schematically illustrated inFIG. 2E. The increased contrast improves defect capture rate of theinspection, especially when a critical dimension of the pattern features216 is small. For example, when a target critical dimension is about 30nm, a pattern feature is considered defective when the measured patternfeature is greater than about 43 nm.

In operation 130, the inspection images may be analyzed to detectdefects. FIGS. 2F-2H schematically illustrate typical defects in apattern feature. FIG. 2F shows a pattern feature 216 a having a criticaldimension, i.e., diameter, larger than a critical dimension of a targetpattern feature 218. An inspection tool having an image capture device,such as a CCD camera, and an image analyzing module, may be used tocapture images of the pattern features 216 and detect any defects. Theinspection tool may be a metrology tool, such as broadband plasma defectinspection tool, laser scanning inspection tools, light emitting diode(LED) scanning tools, or other suitable imaging inspection tools

The inspection tool may include an inspection application to determinethe difference between the critical dimension of the pattern feature 216a and the critical dimension of the target pattern feature 218. In theexample of pattern feature 216 a, the critical dimension is a diameterof the pattern feature 216 a. The inspection application may analyze acaptured image including the pattern feature 216 a to extract thepattern feature 216 a from the captured image and determine a criticaldimension of the pattern feature 216 a using image processingtechnologies. When the critical dimension of the pattern feature 216 ain the inspection image is larger than the critical dimension of thetarget pattern feature 218 by a threshold level, the pattern feature 216a may be determined to be an oversize critical dimension type defect.The threshold value may be in a range from about 20% to about 40%. Inone embodiment, the threshold value may be about 30%. In other words,when a pattern feature being inspected has a critical dimension at least30% greater than the target critical dimension, the pattern feature isconsidered defective. For example, when a target critical dimension isabout 30 nm, a pattern feature is considered defective when the measuredpattern feature is more than about 40 nm.

FIG. 2G shows a pattern feature 216 b having a critical dimension, i.e.diameter, smaller than the critical dimension of the target patternfeature 218. An inspection application may be used to determine thedifference between the critical dimension of the pattern feature 216 band the critical dimension of the target pattern feature 218. When thecritical dimension of the pattern feature 216 b in the inspection imageis smaller than the critical dimension of the target pattern feature 218by a threshold level, the pattern feature 216 a may be determined to bean undersize critical dimension type defect. The threshold value may bein a range from about 20% to about 40%. In one embodiment, the thresholdvalue may be about 30%. In other words, when a pattern feature beinginspected has a critical dimension at least 30% smaller than the targetcritical dimension, the pattern feature is considered defective.

FIG. 2H shows two pattern features 216 and 220 that are connected toeach other or a distance separating two pattern areas is smaller than athreshold value, thereby forming an intrusive type defect. An inspectionapplication may be used to determine whether two neighboring patternfeatures have an intrusive type defect. For example, when the distanceseparating two pattern features is smaller than about the criticaldimension of the pattern features, an intrusive type defect is detectedbetween the two pattern areas. When unintended connection betweenneighboring pattern features are detected, the pattern features areconsidered defective with an intrusive type defect.

In operation 135, remedial processes may be performed when defects, suchas oversize critical dimension type defect, undersize critical dimensiontype defect, and intrusive type defects, are detected. Remedialprocesses may be performed for processes in used in operation 105, forexample, recalibrating the photolithography tool, realignment of aphotolithography mask, and readjusting exposure and developing recipes.

In some embodiments, operations 110, 115, 120, 125, and 130 may beperformed periodically on a sample substrate from a production substratestream for spot checking. In some embodiments, the inspected substratemay be discarded after operations 125 and 130. In other embodiments,when no defects are detected in operation 130, operations 140 and 145may be performed to return the inspected sample substrate back to theproduction substrate stream.

In operation 140, the dummy filling material 214 may be removed frompattern feature 212. The dummy filling material 214 may be removed by anashing process, a wet etching process, or a selective dry etchingprocess. In one embodiment, when the dummy filling material 214 is aBARC material, an ashing process using oxygen plasma may be used toremove the dummy filling material from the pattern feature 212. In otherembodiment, a wet etching process may be performed to selectively removethe dummy filling material 214 when the dummy filling material 214 is asilicon based material, a metal oxide, a silicon nitride, a metalnitride or a metal. In other embodiments, the dummy filling material 214may be removed using a selective dry etch when the dummy fillingmaterial 214 is a silicon based material, a metal oxide, a siliconnitride, a metal nitride or a metal.

FIG. 2I shows the semiconductor structure 200 after the dummy fillingmaterial 214 has been removed. In FIG. 2I, the pattern feature 212 hasnot been formed as deep as the intended depth for production substrates.In one embodiment, an etch process may be performed to etch the patternfeature 212 through the first structure layer 204 using the secondstructure layer 206 as a hard mask. FIG. 2J shows complete patternfeatures 222.

In operation 145, the semiconductor structure 200 is returned toproduction stream and the pattern features 222 may be filled with aproduction material. The production material indicates the intendedmaterial for the pattern features 222 in production substrates so thatthe semiconductor structure 200 can function as designed. For example,when the pattern features 222 are vias in an interlayer dielectric, theproduction material may be a metal, such as copper. In some embodiments,the pattern feature 222 may be a trench or a via for interlayerconnection, and may be filled with copper 224 by the productionoperations. In other embodiments, the pattern features 222 may be a gatecontact for a transistor, and may be filled with a conductive material,such as copper.

Embodiments of the present disclosure provide an improved method forprocess defect inspection. After pattern features are formed in astructure layer, a dummy filling material having dissimilar opticalproperties from the structure layer is filled in the pattern features.The dissimilar optical properties between materials in the patternfeatures and the structure layer increase contrast in images captured byan inspection tool, thus increasing the defect capture rate. Theinspection methods according to the present disclosure improving defectcapture rates particularly when the structure layer includes materialshaving optical properties similar to air, and when the criticaldimension of the pattern features is small, such as smaller than 30nanometer.

Some embodiments provide a method for inspecting defects after aphotolithography process. The method includes etching a structure layerunder a patterned photoresist layer to transform pattern features fromthe patterned photoresist layer to the structure layer, wherein thestructure layer comprises a first material, filling the pattern featuresin the structure layer with a dummy filling material, wherein the firstmaterial and the dummy filling material have dissimilar opticalproperties, exposing a top surface of the structure layer containing thefirst material and the pattern features containing the dummy fillingmaterial, and inspecting the top surface for defective pattern featuresusing an inspection tool.

Some embodiments provide a method for manufacturing a semiconductordevice. The method includes forming a first structure layer over asubstrate, forming a second structure layer over the first structurelayer, wherein the second structure layer comprises a first material,applying a photoresist layer over the second structure layer, patterningthe photoresist layer using a photolithography process, etching throughthe second structure layer and a portion of the first structure layerusing the patterned photoresist layer as a mask to form patternfeatures, filling the pattern features with a dummy filling material,wherein the dummy filling material and the first material havedissimilar optical properties, removing excess dummy filling material toexpose a top surface of the first material and the dummy fillingmaterial, and inspecting the top surface for defects in the patternfeatures.

Some embodiments provide a method for semiconductor processing. Themethod includes forming pattern features in a silicon oxide layer,filling the pattern features with a dummy filling material havingoptical properties dissimilar to silicon oxide, inspecting filledpattern features for defects, removing the dummy filling material fromthe pattern features, and filling the pattern features with a productionmaterial.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of inspecting defects, comprising:forming openings in a underlying layer by using a patterned photoresistlayer as an etching mask, the patterned photoresist layer including atleast one defective pattern; forming a filling material layer in theopenings and over an upper surface of the underlying layer; performing aplanarization operation such that the upper surface of the underlyinglayer is exposed and the filling material layer remains in the opening;and performing an inspection operation to find a defective pattern inthe underlying layer using an optical inspection tool.
 2. The method ofclaim 1, wherein the planarization operation includes a chemicalmechanical polishing (CMP) operation.
 3. The method of claim 2, whereinthe filling material comprises an organic bottom anti-reflective coating(BARC) material.
 4. The method of claim 3, wherein the forming thefilling material layer comprises spin coating the BARC material over theunderlying layer.
 5. The method of claim 2, wherein the underlying layercomprises at least one of amorphous silicon, silicon nitride, aluminumoxide or hafnium oxide.
 6. The method of claim 1, wherein the fillingmaterial comprises at least one of silicon oxide, amorphous silicon,silicon nitride, aluminum oxide or hafnium oxide.
 7. The method of claim6, wherein the underlying layer includes a conductive material layer. 8.The method of claim 6, wherein the filling material is formed by one ofan atomic layer deposition (ALD) process, a chemical vapor deposition(CVD) process, or a physical vapor deposition (PVD) process.
 9. A methodof manufacturing a semiconductor device, comprising: forming a firstlayer over a substrate; forming a second layer over the first layer;patterning the second layer and the first layer to form openings byusing a patterned photoresist layer as an etching mask, the openingspass through the second layer; forming a filling material layer in theopenings and over an upper surface of the underlying layer; performing aplanarization operation such that the upper surface of the underlyinglayer is exposed and the filling material layer remains in the opening;and performing an inspection operation to find a defective pattern inthe underlying layer using an optical inspection tool.
 10. The method ofclaim 9, wherein the performing the inspection operation comprisesselecting an inspection wavelength or inspection spectrum by comparingattenuation coefficients, relative permittivities, or reflectioncoefficients between the filling material and the second layer.
 11. Themethod of claim 9, wherein the openings do not pass through the firstlayer.
 12. The method of claim 9, wherein a reflection of the fillingmaterial with respect to an inspection light of the optical inspectiontool is higher than a reflection of the second layer with respect to theinspection light.
 13. The method of claim 9, wherein a reflection of thefilling material with respect to an inspection light of the opticalinspection tool is lower than a reflection of the second layer withrespect to the inspection light.
 14. The method of claim 9, wherein theunderlying layer includes a metallic material layer.
 15. The method ofclaim 14, wherein the filling material comprises at least one of siliconoxide, amorphous silicon, silicon nitride, aluminum oxide or hafniumoxide.
 16. The method of claim 15, wherein the filling material isformed by one of an atomic layer deposition (ALD) process, a chemicalvapor deposition (CVD) process, or a physical vapor deposition (PVD)process.
 17. A method for semiconductor processing, comprising: formingpattern features in an underlying layer; filling the pattern featureswith a dummy filling material; selecting an inspection wavelength orinspection spectrum by comparing attenuation coefficients, relativepermittivities, or reflection coefficients between the underlying andthe dummy filling material; inspecting filled pattern features fordefects by using the selected inspection wavelength or inspectionspectrum.
 18. The method of claim 17, wherein the underlying layer ismade of silicon oxide and the filling material is an organic material.19. The method of claim 18, wherein the inspection spectrum is between250 nm and 280 nm.
 20. The method of claim 17, wherein a criticaldimension of the pattern features inspected is less than 30 nanometers.